Various types of batteries have been developed heretofore, and in every battery, a packaging material is an essential member for sealing battery elements such as an electrode and an electrolyte. Metallic packaging materials have often been used heretofore as battery packaging materials, but in recent years, batteries have been required to be diversified in shape and to be thinned and lightened with improvement of performance of electric cars, hybrid electric cars, personal computers, cameras, mobile phones and so on. However, metallic battery packaging materials that have often been heretofore used have the disadvantage that it is difficult to keep up with diversification in shape, and there is a limit on weight reduction.
Thus, a film-shaped laminate with a base material layer, an adhesive resin layer, a metal layer and a sealant layer laminated in this order has been proposed as a battery packaging material which is easily processed into diversified shapes and is capable of achieving thickness reduction and weight reduction (see, for example, Patent Document 1). The film-shaped battery packaging material is formed in such a manner that a battery element can be sealed by heat-welding the peripheral edge by heat sealing with the sealant layers facing each other.
The battery packaging material is molded with a mold at the time of enclosing a battery element, and is provided with a space for storing the battery element. During the molding, the battery packaging material is extended, so that cracks and pinholes are easily generated in a metal layer at a flange portion of the mold. Particularly, in recent years, a further thin battery packaging material has been desired as the battery has been required to have a reduced size and thickness. Thus, the above-mentioned problem has been increasingly encountered.
For solving the above-mentioned problem, a method has been generally employed in which an unsaturated fatty acid amide is added to a sealant layer, and thinly bled to a sealant surface, so that slippage is exhibited. A method is also known in which a coating layer of a lubricant is formed on a surface of a base material layer situated as an outermost layer of a battery packaging material to improve slippage of the base material layer. Similarly, it is conceivable that a coating layer of a lubricant is formed on a surface of a sealant layer situated as an innermost layer of a battery packaging material. When such a method is employed, the battery packaging material is easily drawn in the mold during molding, so that cracks and pinholes in the battery packaging material can be suppressed.
However, the unsaturated fatty acid amide relatively easily moves in a sealant layer of polypropylene etc., and ease of movement in the sealant layer depends particularly on a storage environment. For example, when the battery packaging material is stored at a high temperature of about 40° C. or higher, the unsaturated fatty acid amide penetrates into a sealant layer. As a result, slippage of a surface of the sealant layer may be reduced, leading to deterioration of moldability. On the other hand, when the battery packaging material is placed at a low temperature equal to or lower than room temperature, the saturated solubility of the unsaturated fatty acid amide in the sealant layer is reduced. Thus, a large amount of the unsaturated fatty acid amide may be bled out to a surface of the sealant layer, and deposited as a white powder to a processing apparatus such as a mold, resulting in marked deterioration of productivity.
Due to the above-mentioned problem, it is difficult to prevent the deterioration of moldability and troubles associated with a white powder while maintaining a constant added amount throughout a year. When a coating layer is separately formed on an outermost layer or innermost layer of the battery packaging material, the above-mentioned problem hardly occurs, but there is the disadvantage that the production cost increases.